The disclosure relates generally to optimizing performance of a wireless distribution system (WDS), and more particularly to enhancing WDS system capacity by reducing radio frequency (RF) interference among multiple users and among multiple antenna.
Wireless customers are increasingly demanding digital data services, such as streaming video signals. At the same time, some wireless customers use their wireless communications devices in areas that are poorly serviced by conventional cellular networks, such as inside certain buildings or areas where there is little cellular coverage. One response to the intersection of these two concerns has been the use of DASs. DASs include remote units configured to receive and transmit communications signals to client devices within an antenna range of the remote units. DASs can be particularly useful when deployed inside buildings or other indoor environments where the wireless communications devices may not otherwise be able to effectively receive RF signals from a source.
In this regard, FIG. 1 illustrates a distribution of communications services to remote coverage areas 100(1)-100(N) of a WDS provided in the form of a DAS 102, wherein ‘N’ is the number of remote coverage areas. These communications services can include cellular services, wireless services, such as RF identification (RFID) tracking, Wireless Fidelity (Wi-Fi), local area network (LAN), and wireless LAN (WLAN), wireless solutions (Bluetooth, Wi-Fi Global Positioning System (GPS), signal-based, and others) for location-based services, and combinations thereof, as examples. The remote coverage areas 100(1)-100(N) may be remotely located. In this regard, the remote coverage areas 100(1)-100(N) are created by and centered on remote units 104(1)-104(N) connected to a central unit 106 (e.g., a head-end equipment, a head-end controller, or a head-end unit). The central unit 106 may be communicatively coupled to a signal source 108, for example, a base transceiver station (BTS) or a baseband unit (BBU). In this regard, the central unit 106 receives downlink communications signals 110D from the signal source 108 to be distributed to the remote units 104(1)-104(N). The remote units 104(1)-104(N) are configured to receive the downlink communications signals 110D from the central unit 106 over a communications medium 112 to be distributed to the respective remote coverage areas 100(1)-100(N) of the remote units 104(1)-104(N). Each of the remote units 104(1)-104(N) may include an RF transmitter/receiver and at least one respective antenna 114(1)-114(N) operably connected to the RF transmitter/receiver to wirelessly distribute the communications services to client devices 116 within the respective remote coverage areas 100(1)-100(N). The remote units 104(1)-104(N) are also configured to receive uplink communications signals 110U from the client devices 116 in the respective remote coverage areas 100(1)-100(N) to be distributed to the signal source 108. The size of each of the remote coverage areas 100(1)-100(N) is determined by the amount of RF power transmitted by the respective remote units 104(1)-104(N), receiver sensitivity, antenna gain, and RF environment, as well as by RF transmitter/receiver sensitivity of the client devices 116. The client devices 116 usually have a fixed maximum RF receiver sensitivity, so that the above-mentioned properties of the remote units 104(1)-104(N) mainly determine the size of the respective remote coverage areas 100(1)-100(N).
The client devices 116 in any of the remote coverage areas 100(1)-100(N) may be running bandwidth-hungry applications, such as high-definition (HD) mobile video, virtual reality (VR), and augmented reality (AR), that drive the demand for high-capacity wireless access. Moreover, multiple client devices 116 may be running such bandwidth-hungry applications concurrently, thus further increasing the demand for data throughput in each of the remote coverage areas 100(1)-100(N). As a result, the wireless communications industry has adopted multiple-input multiple-output (MIMO) technology to help meet the increasing bandwidth demand by the client devices 116. In this regard, each of the remote units 104(1)-104(N) may employ multiple antennas to distribute multiple streams of the downlink communications signals 110D concurrently. For example, each of the remote units 104(1)-104(N) may employ two antennas to concurrently transmit two streams of the downlink communications signals 110D, thus doubling the data throughput in the remote coverage areas 100(1)-100(N). When the remote units 104(1)-104(N) distribute the multiple streams of the downlink communications signals 110D concurrently to multiple client devices 116, the remote units 104(1)-104(N) are said to be communicating the downlink communications signals 110D based on multiuser MIMO (MU-MIMO) technology.
The MU-MIMO technology can help provide increased data rate/throughput, enhanced reliability, improved energy efficiency, and/or reduced interference in the remote coverage areas 100(1)-100(N). As such, the MU-MIMO technology has been incorporated into recent and evolving wireless communications standards, such as long-term evolution (LTE) and LTE-Advanced. However, to fully benefit from the enhancements provided by the MU-MIMO technology, each of the multiple client devices 116 needs to employ an equal number of antennas as the remote units 104(1)-104(N). Unfortunately, it may become more difficult to add additional antennas in the client devices 116 due to space limitations and complexity. As a result, it may become difficult to scale the MU-MIMO technology beyond the capabilities of the client device 116. Accordingly, the wireless communications industry is adopting a new antenna technology known as massive MIMO (M-MIMO), which may scale up the MU-MIMO technology by orders of magnitude, to meet the increasing bandwidth demands by the client devices 116.
No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinency of any cited documents.